In general, styrene copolymers have excellent moldability, rigidity and electrical properties, and have been widely used in various industrial fields including OA equipment such as computers, printers and copy machines, home appliances such as televisions and audios, electrical and electronic components, automobile components, miscellaneous goods and the like. Particularly, heat-resistant styrene copolymers having favorable resistance at high outside temperatures by enhancing heat resistance have been used for particular applications such as housing for home appliances and automobile interior materials.
α-Methyl styrene (AMS) is commonly used in order to obtain a styrene copolymer having high heat resistance. α-Methyl styrene is relatively inexpensive and has excellent heat resistance, but is polymerized at a temperature lower than polymerization temperatures of existing styrene copolymers due to a low ceiling temperature (Tc), and accordingly, has a problem in that conversion rate significantly decreases. A low conversion rate is directly related to a productivity decrease, and as a result, is a great obstacle in industrial applications.
Accordingly, in order to readily apply a heat-resistant styrene copolymer to industry, a technology that does not decline mechanical and chemical properties originally possessed by a heat-resistant styrene copolymer while increasing productivity by complementing a disadvantage of a low ceiling temperature of α-methyl styrene and enhancing a conversion rate of the heat-resistant styrene copolymer, that is, a technology enhancing a conversion rate and not causing deformation to an original heat-resistant styrene copolymer has been required.
In view of the above, the inventors of the present invention have studied on methods not affecting mechanical and chemical properties possessed by the heat-resistant styrene copolymer while increasing productivity by enhancing a conversion rate of the copolymer, and have identified that, after a heat-resistant styrene copolymer is prepared through mass-polymerization by adding a small amount of vinyl imidazole to α-methyl styrene and acrylonitrile, which compose common existing heat-resistant styrene copolymers, and is analyzed, a conversion rate of the heat-resistant styrene copolymer is enhanced without causing physical property changes, and have completed the present invention.